Method of decreasing metal corrosion



Patented July 15, 1941 METHOD OF DECREASING METAL CORROSION Carroll J.Wilson, Hillside, and Charles E. Morrell, Elizabeth, N. 1., assignors toStandard Oil 1 Development Company, a corporation of Delaware NoDrawing. Application December 3, 1938, Serial No. 243,764

10 Claims. (01. 252-52) This invention relates to a process fordecreasing corrosion of metals in contact with viscous hydrocarbonoil-s. More particularly, it relates to the use of relatively stableorganic peroxides in lubricating oil to inhibit chemical solution ofcopper and similarly corrodible metals by lubricating oils so as todecrease the transfer of the dissolved metal to other parts of a machinelubricated by the oils.

Corrosion of lubricated parts of machines and deposition of metalliccopper in the form of even sliced film on ferrous parts has been aserious problem in the refrigerator industry because the deposited metaltends to cause seizure of moving parts i. e. tightly fitting slidingparts, and faulty valve action. From the extensive research on thisproblem, several causes of chemical solution of copper in lubricatingoil and its transfer to surfaces of the machine promoting faulty actionhave been indicated. There is evidence to support the view thatlubricating oils having a high Sligh oxidation test, which is a measureof sludge formed by oil exposed to oxygen for a definite period of timeat a specific elevated temperature, for example, 392 F., have arelatively high corroding power. high oxidizing tendency has beenexplained as being due to .fatty acids formed by oxidation of the oils,but the oxidation sludge forming tendency or acid content of an oil hasbeen found not to be the sole factor in the corrosion of copper.

There is also'some evidence that the presence of sulfur compounds inoils tends to increase their corrosive action. Another possible factoris the presence of moisture. Although previously, an oil was selected ashaving low copper solubility and plating tendencies on the basis that itwas highly refined and had a low Sligh number sludging property, thismethod of selection wa not found entirely satisfactory. In addition,very highly refined oils may have less lubricating value, are morecostly, and in spite of their low Sligh numberfstill may show highsolubility for copper.

Dissolution of copper by oils with by the oils regardless of whether thelubricating oil has been highly refined and contains no appreciableamount of sulfur compounds or whether the lubricating oil has not beenhighly refined and retains its original oiliness. In accordance with thepresent invention, substances which have been found to have excellentinhibiting properties are the relatively stable peroxides, which for themost part are aromatic peroxides, in particular tetralin peroxide.

As a general rule the aliphatic peroxides are unstable and cannot besafely handled nor can they be maintained in the oil under conditions towhich the oil is subjected. Some few exceptions exist of aliphaticperoxides which may be used in oils at low temperatures. Triacetoneperoxide is one of the more stable aliphatic peroxides. But, in general,the more stable peroxides are aromatic, e. g., naphthalene peroxide,tetralin peroxide, ascarldole, and benzoyl peroxide. Stability, ofcourse, is considered with reference to the conditions under which thecompound is employed. With reference to refrigerating compressorlubricants or lubricants used in similar services the peroxides shouldbe substantially stable at temperatures ranging to about 212 F. In someinstances, stability to even higher temperatures may be desired. The wayin which these inhibitors are employed and the experimental technique bywhich they are tested for proving their effectiveness will be fullyunderstood from the following description.

A spiral of copper wire was immersed in a test tube filled with the oilto be tested, then kept in an oven at 200 F. Periodically, samples ofthe oil were removed from the tube and tested for dissolved copper bythe dithizone method of analysis. This test depends upon the intensityof violet color developed by copper dithizonate in carbon tetrachloridesolution. After the 011 sample containing the immersed copper wire coilof specified size (36 inches of No. 22 copper wire cleaned by sodiumcyanide solution followedby successive washing with water then methanol)has been heated at 200 F. for a definite period, one cc. of the oil wasanalyzed using the following procedure:

Dissolved copper is leached from the withdrawn one co. sample with a 10%aqueous solution of sulfuric acid. Copper isthen extracted from thisacid solution with a 0.006% solution of diphenyl thiocarbazone'(dithizone) in carbon tetrachloride. Upon doing this, if an appreciablequantity of copper is present, a color change from green to violet isnoted. Excess diphenyl thiocarbazone is removed from the carbontetrachloride-copper diphenyl thiocarbazone solution with dilute ammonia(5 cc. of concentrated aqua ammonia per liter) and the violet color ofthe resultant copper diphenyl dicarbazonate solution may then be matchedwith a standard solution of this compound of known concentration todetermine the amount of copper dissolved by the oil. If no appreciableamount of copper is disto be used for improving various lubricating oilsis seldom outside the limits of 0.02% to 1% by weight. The exactconcentration will depend somewhat upon the characteristics of the oilitself. Usually, about 0.1% to 0.5% of the inhibitor is suflicient.Lubricating oils which in service are contacted with parts containingmetals having solution tendencies, such as copper, are particularly tobe given a lower copp r solubility.

solved by the oil, no change of color from green These conditions existcommonly in the lubrito violet occurs in the dithizone solutionindication of refrigerating compressors and electrical eating that lessthan about 5 mg. per litre apparatus wherein copper has to be employed(0.005%) of copper was dissolved by the oil because of its highductility, heat conducting tested. and electricity conductingproperties. The These tests were run under comparable condilubricantsusually employed in these services are tions, the test temperature beingheld as closely straight mineral oil distillates having Saybolt constantas possible, exposure to air being viscosities ranging from about 100 to400 seconds avoided, and the dithizone reagent being of at 100 F., andpreferably refined by usual acid, constant quality by being freshlyprepared and clay, or selective solvent treatments to improve, kept indark bottles. The period of heating the primarily, their color andviscosity characteristest sample in the presence of the copper Wiretics; but even the relatively pure synthetic hydrobefore the dissolvedcopper concentration was carbon lubricants are similarly susceptible tosuflicient to give the green to violet color change improvement againstoxidation and attendant in the dithizone solution was considered thecorrosiveness as is shown in the table of results. life of the oil. Thefollowing table illustrates the Instead of depending solely on thepreferred relative effectiveness of the various agents added peroxideinhibitors, other types of oxidation and to oils subjected totheforegoing test. Three corrosion inhibitors may be used in combinationvarieties of lubricating oils were used and the with very good results.Also, other addition relative inhibiting power of compounds typifyingagents may be simultaneously employed, such as, peroxides, amines, andphenols were observed: oiliness agents, sludge dispersers, viscosity im-Life in Lubricating 011 Color tgeliilllll, 0.1% of inhibitor hours 21Highlyrefined petroleum distillate Whi-e 0.10 igg' 475 27 Tetralinperoxide" 115 Medium refined petroleum distillate Pale yellow... 0.25Benzoyl peroxide 92 Dlphenyl amine 48 Beta-naphthoL. 48 Synthetichydrocarbon lubricant 0. 8 t -a a From the tabulated results it canreadily be seen that the organic peroxides are much more effective thanthe other types of compounds which also showed good inhibitingproperties. The effectiveness of tetralin peroxide is preeminent.

Exactly what effect the inhibitors have on the lubricating oils indiminishing the corrosive action of the oils on the metals is diflicultto determine, The peroxides, which are compounds containing two oxygenatoms linked together and each being linked to a difierent carbon atomin a molecule, have hitherto been known as powerful oxidizing agents orpro-oxidants, but in lowering the copper'solubility of an oil theyappear to confer upon the oil a characteristic which has generally beenidentified with low sludge forming oils.

Judging from their copper discoloration test, oils which were improvedin regard to lower corrosive effects on copper contained no free sulfur,and even some which were so highly refined as to have very loworganically combined sulfur contents were also improved in the samerespect by the added inhibitor. These results may be interpreted asindicating that the inhibitor lowers both the oxidation of the oil andthe deleterious action of any combined sulfur compounds. It is moreimportant to consider the practical fact that the inhibitor decreasesthe dissolving power of the oil on such metals as copper.

In general, the amount of preferred inhibitors more effective than eiher ingredient separately 1 I in lowering corrosion by some lubricatingoils. From all indications, the preferred peroxide corrosion inhibitorsshould be beneficial in counteracting any corrosive tendency in the useof additional agents, such as fatty acid esters or soaps, orsulfur-containing compounds.- These considerations are of value inmaking the peroxide corrosion inhibitors also valuable for improvingslush'ing oils, hydraulic fluids, greases, etc.

This invention is not to be' limited by any theoretical explanationpresented herein, or by the examples, all of which are given by way ofillustration, but only by the following claims which are intended toclaim all novelty inherent in this invention.

We claim:

1. The method of decreasing the corrosion of a metal in contact with alubricant which com- 3. The method of lowering the copper solubility ofa lubricating oil which comprises incorporating about 0.2% to 1% of anaromatic peroxide in the oil.

a slight tendency to corrode metals such as copper comprising alubricating oil and a small amount of a stable oil-soluble organicperoxide added as a corrosion inhibitor.

5. A refrigerator compressor lubricating oil having low copper corrosiontendencies which comprises a hydrocarbon lubricating oil having aSaybolt Viscosity in the range of 100 to 400 seconds at 100 F. and asmall amount of an added stable oil-soluble organic peroxide inhibitor.

6. A lubricating oil as described in claim 4 in which tetralin peroxideis said inhibitor.

7. A lubricating oil composition stabilized against copper corrosiontendencies of any organically combined sulfur constituents present andoxidation efiects which comprises a major proportion of minerallubricating oil and a small amount of an added stable oil-solubleorganic peroxide inhibitor.

4. An improved lubricating composition having 8. A refrigeratingcompressor lubricating oil having low copper corrosion tendencies whichcomprises a refined hydrocarbon lubricating oil having a Sayboltviscosity at 100 F. in the range of 100 to 400 seconds and containing no,free sulfur and about .1% to 5% of tetralin peroxide.

9. A lubricant comprising a substantial amount of mineral lubricatingoil, a small amount of an oxidation inhibitor selected from the groupconsisting of aromatic amines and phenols, and a small amount oftetralin peroxide.

10. A lubricant comprising essentially a petroleum oil having a life notsubstantially more than 27 hours before dissolving 0.05% of copper whenheated in contact with a copper wire coil substantially as described,said lubricant having added thereto a suflicient amount of a .stableoil-soluble organic peroxide corrosion inhibitor to raise the life ofthe blend to at least about 115 hours.

CARROLL J. WILSON, CHARLES E. MORRELL.

